This invention relates to an on-line terminal unit used for firm banking and the like. Firm banking is a service of a bank based on an on-line computer system in which a computer of the bank is connected to computers of firms through a communication line, thereby having various transactions with the firms and offering information to the firms.
Conventional on-line terminal units intended for this purpose are generally equipped with a security function which makes the unit operative in response to the entry of a secret number which is known only by a legitimate user. However, this conventional security function involves such problems that if the secret number is leaked to another person, the terminal unit can illegally be operated by that person, or if the legitimate user forgets the secret number, the user cannot operate the terminal unit.
Another conventional security function, as described in Japanese Patent Unexamined Publication No. 1-217675, is designed to record and update the date and time of line disconnection in the customer's record in the customer files stored in the terminal unit and in the central computer at each information access event made through the terminal unit, thereby protecting the account transaction information from being accessed by other person through a terminal unit. However, this preventive function for firm banking against erroneous terminal connection is solely intended to prevent illegal information access from terminal units other than authorized terminal units, and it cannot prevent an illegal information access through an authorized terminal unit.